1. Field of the Invention
The present invention relates to a forging process for titanium alloys, more particularly to a process for preventing an oxide layer from forming during a forging process for titanium alloys.
2. Description of the Related Art
Recently, the development of a lower fuel consumption and pollution-preventive automobile has been one of the most important goals for the automotive industry.
In general, improving engine performance, improving heat resistance, reducing the weight of engine components, and reducing the running resistance and the weight of the body can improve the fuel efficiency of an automobile internal combustion engine. Improving the engine performance and the heat efficiency can be more easily and directly attained by reducing the weight of engine components, especially reciprocating components such as connecting rods and pistons, rather than reducing the weight of the body. Accordingly, this area has been the focus of a great deal of research and development.
Engine performance and fuel efficiency can be improved by using a light-weight material to reduce an engine component's inertia, thereby reducing friction losses. Titanium alloys having high hardness to weight ratios are good candidate materials for engine components.
In the aerospace industry, titanium is used for light-weight components such as aircraft body frames and wings and jet engine turbine blades because of its excellent heat resistance and hardness.
Although titanium has superior hardness and heat resistance, it is so expensive in comparison to aluminium that its use has been limited. Recently, however, as improved smelting method has been developed and new resource materials have been discovered, the price of titanium has decreased so as to become feasible for widespread use in the automotive industry. Accordingly, many kinds of titanium alloys have been developed for an automotive transmissions and engines which must endure high temperature and mechanical stress.
For example, a titanium alloy containing 10 wt % of vanadium, 2 wt % of iron, and 3 wt % of aluminium is hard and easily forged, a 15-3 titanium alloy containing 15 wt % of vanadium and 3wt % of chromium, aluminium, and tin can be rolled at an ambient temperature, and a titanium alloy containing 2 wt % of vanadium, 2 wt % of tin, 4 wt % of zinc, and 2 wt % of molybdenum exhibits a high temperature resistance.
Japanese Laid-Open Patent No. 89-95837 discloses a process for preparing a .beta.-type titanium alloy material wherein descaled .beta.-type titanium alloy is blasted, zinc-phosphated, washed with water, treated with a reaction-type metal soap, dried and cold-forged.
These titanium alloys, however, form an oxide layer of TiO or TiO.sub.2 which weakens the fatigue strength of the alloy.